1. Field of Invention
This invention, a near electrode imager, relates to a near-electrode imager with nuclear magnetic resonance (NMR) sensitivities for providing a direct in-situ analysis of an electrochemical process in order to determine such phenomena as the composition of an electrode-electrolyte interface, ion penetration depths within advanced synthetic electrode materials, and ion concentration gradients within solid state batteries.
2. Description of Related Art
The near-electrode imager provides a direct in situ spectroscopic method to probe the fundamental-ion transport process in advanced battery materials and the detailed chemical composition of the electrode-electrolyte interface. The near-electrode imager uses the radio frequency (RF) gradient within a cylindrical toroid cavity to provide high-resolution nuclear magnetic resonance (NMR) spectral information on electrolyte materials as a function of radial distance from the working electrode of a battery or fuel cell. With a spacial resolution near 1.0 micron, the new imager has resolving power nearly two orders of magnitude higher than conventional MRI while still retaining NMR chemical shift information, which is lost in conventional magnetic resonance imaging (MRI) measurements. The result is a three dimensional plot (or image) of NMR signal intensity and chemical shift versus radial distance from the central working electrode. Significantly, the chemical-shift information allows chemical species to be distinguished from one another. Thus, it becomes possible to follow reaction pathways that may exist in different parts of the cell, most notably at the important electrode-electrolyte interface. In addition, the theoretical spacial resolution of the near-electrode imager is better than possible with MRI because of the stronger gradient that is intrinsic to the torus. Further, spacial resolution with the near-electrode imager is less dependent on the line widths of the NMR signals used in the measurements. This factor is particularly significant for polymer electrolytes (such as those used in lithium-polymer batteries), whose broad NMR lines would limit the resolution of conventional MRI techniques to .gtoreq.50 .mu.m. The high spacial resolution and the ability to retain NMR spectral information combine to make the near-electrode imager nearly ideal for the investigation of fundamental processes in battery and fuel cells. The near-electrode imager provides for the systematic investigation of the fundamental reaction chemistry that has not been previously possible with alternative analysis techniques.
The near-electrode imager provides a direct in situ spectroscopic means to probe the composition of the electrode-electrolyte interface and ion penetration depths within advanced synthetic electrode materials. In addition, the device may be used to investigate the fundamental chemical and physical properties that influence the ion transport mechanisms in the current generation of battery materials. The imaging technique is well suited to measure ion concentration gradients within solid state batteries, diffusion coefficients at different locations in a working cell, conformational dynamics of polymer electrolytes, and changes in phase composition.
This invention relates to an improved method and apparatus for NMR imaging, and in particular, to an apparatus that provides in situ NMR chemical shift, distance, and mobility information for species that are located on, within, and around the electrodes in electrochemical processes. The near-electrode imager provides complete high-resolution nuclear magnetic resonance (NMR) spectra as a function of distance away from the working electrode of a battery or fuel cell. The near-electrode imager utilizes the rotating frame imaging (RFI) method of data collection and the intrinsically strong radio frequency (RF) field gradients produced within toroid cavity resonators to provide spacial resolution near 1.0 micron. Importantly, this imaging technique retains the chemical shift information that is typically sacrificed in conventional MRI measurements. Consequently, the near-electrode imager has the ability to follow reaction pathways because it allows individual chemical species to be distinguished on the basis of their NMR chemical shifts and coupling constants. In addition, the near-electrode imager has been demonstrated to retain the capability to determine spin relaxation mechanisms. This latter capability makes it possible to probe mobilities and the phase composition of polymer electrolytes in the electrolyte depletion zones that form adjacent to the electrodes during normal battery operation. The near-electrode imager can examine ion concentration gradients in working electrochemical cells.
The imager system provides for a toroid cavity nuclear magnetic resonance (NMR) detector capable of quantitatively recording radial concentration profiles, diffusion constants, displacements of charge carriers, and radial profiles of spin-lattice relaxation time constants.
It is the object of this invention to provide an apparatus for employing nuclear magnetic resonance techniques to materials to provide an analytical profile of phenomena associated with electrochemical and other processes on a real-time basis.
It is a further object of this invention to provide a method of employing the imaging apparatus to investigate the fundamental chemical and physical properties that influence ion transport mechanisms.
It is another object of this invention to provide a method for probing the composition of the electrode-electrolyte interface and ion penetration depths within synthetic electrode materials.
Additional advantages, objects and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.